1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer or a copying machine which is operable in a marginless print mode of printing on a whole surface of a recording material without providing a margin in the recording material.
2. Description of the Related Art
Image forming apparatuses such as printers and copying machines are required to perform marginless print (borderless print) for placing image information on a whole surface of a recording material without providing a margin in the recording material. This is not only because values such as quality of an output matter can be improved but also because there is large cost merit owing to reduction in processing of removing the margin in an after-print processing to meet a user's demand from the standpoint of, for example, a producer of the output matter.
In electrophotographic systems, one of the major factors hindering the realization of the marginless print is a marking back caused by expanded toner. The marking back represents a phenomenon in which, in a case of continuous print, unnecessary toner expanded from a preceding recording material and adhering to a transfer roller is not cleaned up satisfactorily within a short time before a succeeding recording material is conveyed to a transfer portion, so that the unnecessary toner adheres to a back side surface of the succeeding recording material.
Japanese Patent Application Laid-Open No. 2005-215047 discloses an image forming apparatus configured to prevent such a marking back. The image forming apparatus is configured to prevent the marking back from occurring on a succeeding recording material by adjusting a start position of writing of a latent image performed by a writing unit based on a detection result from a deviation detecting unit configured to detect a deviation of the recording material and, after the adjustment, controlling the writing unit to start writing the latent image to a plurality of photosensitive drums.
Further, Japanese Patent Application Laid-Open No. 2007-47474 discloses another image forming apparatus configured to prevent the above-mentioned marking back. In the image forming apparatus, a transfer step is executed when a region of a surface of a conveyor belt configured to convey the recording material to which unnecessary toner due to a marginless image transfer does not adhere is larger than a region thereof which is necessary for an image to be transferred subsequently. When smaller, a cleaning step of cleaning the conveyor belt is executed, to thereby prevent the marking back.
However, in the above-mentioned image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-215047, the marking back can be reduced, but it is difficult to maintain high positional accuracy of the recording material being conveyed even if positional accuracy of the image by the writing unit is improved. It is difficult to constantly maintain a fixed size of the recording material, and hence there is a fear that a problem of generating a margin may occur occasionally.
Further, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2007-47474, the marking back can be reduced, but it is necessary to provide an interval before the succeeding recording material is conveyed if the region to which the expanded toner adheres is large. As a result, there is a fear that a problem of a considerable decrease in the productivity may occur.